1. Field of the Invention
This invention relates generally to methods and apparatus for determining the rate at which a pile driving hammer strikes a pile and more particularly, but not by way of limitation, to methods and apparatus utilizing electronic instrumentation to monitor offshore pile driving hammers used in the oceanic construction of drilling platforms and the like.
2. Description of the Prior Art
In building such structures as offshore drilling platforms it is often necessary to drive structural supports, or piles, by suitable pile driving equipment, such as a pile driving hammer, as is known in the art. Although the same pile driving hammer may be used on different jobs, the optimum rates over time and distance at which the pile driving hammer strikes the pile to drive it into the supporting surface can vary from job to job because the size and strength of the driven pile may differ, the depth to which the pile has been or is to be driven may vary, or the type of soil into which the pile is to be driven may vary, for example. Therefore, to control the quality of operation of the pile driving hammer for the specific job on which it is being used, it is necessary to monitor the hammer to determine if it is striking the pile at the desired rate as determined by the various pertinent factors which can change from job to job. By so monitoring the rate of the pile driving hammer, the hammer can be more efficiently controlled.
This general need for monitoring pile driving operations has been recognized and previous attempts to satisfy it have been made or proposed. For example, one way to monitor the rate at which a hammer strikes a pile is to have a person manually operate a stop watch and counting device so that the number of strikes during a certain time period can be recorded on a chart or in a table, for example. Another means for monitoring the pile driving hammer is to attach a strain gauge to the pile to record the strain in the pile as it is driven into the supporting surface. Also, high speed photography may be used to capture the individual reciprocations of the pile driving hammer as it moves and strikes the driven pile.
Still another type of pile driving monitoring system is disclosed in U.S. Pat. No. 3,498,388 in the name of Jovis. The apparatus disclosed in this patent includes means for comparing the actual rate of the pile driving hammer with a predetermined reference rate and further includes means for providing a tangible recording of the monitored parameters. More particularly, the apparatus is proposed to include an accelerometer affixed to the pile, a rectifier, a monostable multivibrator, a filter, a differential amplifier and a throttle.
U.S. Pat. No. 3,721,095 in the name of Chelminski discloses a controllable force method and system of driving piles which senses pressures in a bounce chamber. As shown in FIG. 4 of the Chelminski patent, the apparatus is proposed to include a pressure transducer which detects the actual pressure in the chamber and a comparator which compares the detected actual pressure with a desired pressure and adjusts the fluid pressure accordingly.
U.S. Pat. No. 4,051,351 in the name of Mallick, Jr. et al. discloses an electronic system for monitoring pneumatic tool performance. The system provides a count of the number of work cycles generated by the pneumatic tool during operation thereof.
U.S. Pat. No. 3,714,789 in the name of Chelminski discloses another type of pile driver method and system.
Although these prior art devices provide pile driving monitoring apparatus, they generally require sensing means to be located either in direct contact with or relatively close to the pile driving hammer and/or pile. Therefore, they do not provide means for simply, quickly and accurately monitoring the blow rate of the pile driving hammer and for obtaining a permanent record of the information derived therefrom when the pile driving hammer is used in building an offshore drilling platform, for example. It is also believed that these devices fail to remotely detect individual strikes of the hammer against the pile. Additionally, it is believed that these previously used or proposed devices fail to provide means for calculating the number of times a pile driving hammer strikes a pile over either a predetermined time period or over a selectable distance of pile movement. It is believed that these devices furthermore do not include the means for entering various types of pile driving hammer data, or other data, into the monitoring equipment.